In the field of medicine, a sample applying system or a sampling system (hereinafter a sampling system) is often needed for sampling and for adding and/or pipetting samples and/or reaction solution. In a sample applying system, the location of the sampling needle is positioned based at least in part on the detection of the liquid level. That is, the sampling system preferably stops advancing the sampling needle or device when the sampling needle contacts the object liquid level so as to carry out the next task. This function may be realized by a liquid level detecting device.
The liquid level detecting device converts capacitance change in the sampling needle into voltage or potential change and determines whether the sampling needle contacts the liquid level based at least in part on this change in capacitance. In operation, because different specific conditions of detecting positions may have different manner or magnitude of influences on the capacitance change of the sampling needle, detection results often vary as well. For example, when the sampling needle enters an environment such as a metal container, the capacitance change of the sampling needle itself is relatively apparent and thus tends to lead to incorrect detection of the liquid level. Whereas in the case of a plastic container or when the container contains relatively little amount of liquid, the capacitance change of the sampling needle is relatively weak or insignificant in comparison to the change in capacitance due to the contact with the liquid surface and thus may result in a lowered sensitivity in detection. This lowered sensitivity in detection of the liquid level often leads to a scenario that no result may be obtained quickly even when the sampling needle has indeed contacted the liquid level.
For sampling systems, particularly sampling systems utilizing the liquid level detecting device, it is desired that the sampling system may both detect liquid level with high sensitivity and avoid incorrect detection in an environment where the container or the amount of liquid in the container may skew the detection. However, it is difficult for conventional liquid level detecting devices to meet such requirements because these conventional liquid level detection devices tend to cause errors in test results when it is needed to perform detection under various complex environments.